import math

x1,y1,x2,y2 = map(float,input().split())

x =math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2) 

print(f'{x:.08f}')


 import math math x1,y1,x2,y2 = map(float,input().split()) x1 map(float,input().split()) map float input().split() ().split () input split y1 x2 y2 x =math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2) x math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2) math.sqrt math sqrt (x2 - x1) ** 2 + (y2 - y1) ** 2 (x2 - x1) ** 2 x2 - x1 x2 x1 2 (y2 - y1) ** 2 y2 - y1 y2 y1 2 print(f'{x:.08f}') print f'{x:.08f}' x1,y1,x2,y2 = map(float,input().split()) map(float,input().split()) x1 y1,x2,y2 = map(float,input().split()) map(float,input().split()) y1 x2,y2 = map(float,input().split()) map(float,input().split()) x2 x =math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2) math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2) x y2 = map(float,input().split()) map(float,input().split()) y2
import math

x1,y1,x2,y2 = map(float,input().split())

x =math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2) 

print(f'{x:.08f}')



